(Applicant's Abstract): Recent studies have documented a sharp rise in the use of"Speed" in the U.S., a pattern that has been implicated in recent increases in the incidence of HIV-1 among men who have sex with men (MSM). While research on "Speed" has increased in recent years, there are a number of questions vital to both epidemiology and prevention that have not yet been adequately assessed. There is also little systematic information about the function and meaning of "Speed" use among MSM, particularly in relation to partner selection and sexual risk practices. Moreover, as yet there is little information available about antecedents to injection initiation. More fundamentally, there is as yet little systematic documentation of the behavioral practices used to prepare and inject "Speed," including variability in practices such as "punding" and "tweaking" that may pose particular risk for viral transmission. These types of data are vital to understanding the epidemiology of viral infection among MSM as well as for the development of targeted prevention messages and strategies. Employing a "controlled comparison" design, and building upon our development of standardized, ethnographic research protocols and virological modeling of transmission risks, we propose a multi-site, study with the following epidemiological objectives: 1) To describe the types of physical settings and social contexts in which the use of "Speed" is prevalent among MSM; 2) To describe the range of forms of "Speed" used by MSM, including pills, powders, "rock," and "crystal," and variability in the modes of administration that are associated with these different forms; 3) To describe the range of behavioral practices MSM use to prepare and inject "Speed," including practices such as "punding," "tweaking," and binge injection that may pose unique risks for transmission of viral pathogens such as HIV, HBV, and HCV; 4) To compare and contrast antecedent factors and social processes associated with initiating use of "Speed" among MSM, with an emphasis on antecedent factors associated with injection initiation; 5) To describe the role of "Speed" in the drug and sex "scripts" of MSM, chiefly with an interest in its influence on sexual partner selection practices and types of sexual transactions.